Switch structures



J. O. MOORHEAD Feb. 18, 1958 SWITCH STRUCTURES 2 Sheets-Sheet 1 Filed Aug. 1, 1956 In yen to;;

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Feb. 18, 1958 J. o. 'MOORHEAD swmcn STRUCTURES v2 Sheets-Sheet 2 Filed Aug. 1, 1956 132 men ton United States Patent SWITCH STRUCTURES John 0. Moor-head, Atfleboro, Mass., assignor to Metals & Controls Corporation, Attleboro, Mass., :1 corporation of Massachusetts Application August 1, 1956, Serial No. 601,501

4 Claims. (Cl. 200-138) This invention relates to electrical switch structures.

In the operation of electrical switch structures which embody coacting electrical contacts, the likelihood may well exist that arcing from one contact to another will occur. Thisphenomenon and its deleterious effects are wellknown in the art, and it is the general purpose of this invention to provide a switch structure which lessens these deleterious eflects.

Accordingly, an object of this invention is to provide an improved electrical device and/ or an improved structural member for an electrical device whereby deleterious effects due to electrical arcing are either prevented or substantially lessened.

Another object of this invention is to provide an improved electrical device by which the intensity of the arcing across its electrical contacts is kept to a minimum.

A; further object of this invention is to provide an electrical device having spaced contacts and a bridging contact member whereby the pressure exerted by the bridging contact member against each of spaced contacts remains; substantially equal with changes in the effective relative heights of the spaced contacts.

'-A further object of this invention is to provide an electrical device having spaced contacts and a bridging contact member whereby separation of the bridging contact mem ber from all of the spaced contacts is accomplished simultane'ously.

Another object of this invention is to provide an improvedcasing or structural member for an electrical device and/or an improved electrical device embodying such a structural member whereby an unintended substantial increasejin the-conductivity along a surfaceof the structuralmember otherwise intendedto be nonconductive is prevented or effectively counteracted.

A furtherobject of this invention is to provide such a structural member and/orsuch an electrical device whereby certain deleterious and objectionable effects of an elec- Fig. 2 is a sectional view taken along line 2-2 of Fig. 1

Fig. 3 is a plan view of the cup-shaped member included in Fig. 1 and against one end of which seats a spring for biasing the contacts toward closed position;

Fig. 4 is a plan view of the bridging contact member included in Figs. 1 and 2;

Fig. 5 is a perspective view of the transfer member included in Figs. 1 and 2;

Fig. 6 is a view similar to Fig. l but showing the con tacts of the device in open position;

Fig. 7 is a sectional view taken along line 77 in Fig. l; and

Fig. 8 is a view similar to Fig. 7 but showing the contacts of the device in open position.

Referring to the drawings, an exemplary construction is shown which takes the form of an automatically resetting, thermally responsive, snap-acting switch 10. Electrical switch 10 includes structural means in the form or" a casing 12 formed of electrically insulating material such as one of the customary molded plastics. A pair of terminals 13, 14 are supported by easing member 12 in any suitable manner. By way of example, casing member 12 may be molded about these terminals. Each of terminals 13, 14 leads to the exterior of the casing member whereby it may be connected to one side of a source of electrical current.

Terminals 13 and 14 provide contacts or contact-forming portions 15 and 16, respectively. Contacts 15 and 16 may be provided with layers or portions 17 and 18, respectively, which are formed of a material having a high electrical conductivity such as silver and which arev suitably bonded to the remainder of these respective contacts. Terminals 13 and 14, except for layers or portions 17 and 18, may be formed of a suitably electrically conductive material such as brass, Monel or copper. A bridging contact member 20 made of, for example, brass, Monel or copper, is disposed adjacent contacts 15 and 16. The contact-forming surface of contact member 20 which cooperates with the adjacent surface of contacts 15 and 16 is formed by a layer or portion 21 of silver or other contact alloy which is suitably bonded to the remainder of contact member 20. As the description proceeds it will become apparent that contact member 20 is engageable and disengageable with both of contacts 15 and 16 electrically to connect and disconnect contacts 15 and 16.

The upperisurface of bridging contact member 20, as

' viewed in Figs. 1 and 3, provides a concavely curved surtri'cally conductive, deposited coating on the structural device which are 'econornical'to manufacture simple,

application of which will be indicated in the following claims.

Inthe accompanying drawings, in which one of the various possible embodiments of the invention are illustrated:

Fig. 1 is a sectional view of an electrical device embodying this invention and showing the contactsof this device in. closed position;

face. 24 which is associated with a convexly curved surface 25 provided by the bottom of a generally cupshaped member 26. At each end of concavely curved surface 24 is located a corner 27, 27. As is apparent from Figs. 1 and 3 convexly curved surface 25 is formed on a greater radius of curvature than depression 24 with the result that surface 25 engages bridging contact member 20 at corners 27, 27. 7

One end of a compression spring 30 is seated in cupshaped member 26 and the other end thereof is seated in a socket 31 provided by casing member 12. Accordingly, spring 30 resiliently biases contact or contact member 20 against contacts 15 and 16. It will be noted that spring 30 is confined only at its ends, and that it is laterally displaceable in socket 31 whereby it is free to seek an adjusted position if so constrained due to lateral displacement of bridging member 20. Also it will be noted that each end of spring 30 is formed so that the respective end turns of the coil lie substantially perpendicular to the opposite directions of flexure of the spring during operation of the switch 10. Since the portion of cup-shaped member 26 against which spring 30 seats is flat, it is clear that member 26 is resiliently biased by this spring against pivotal movement.

Asis apparent in Fig. 1, the open end of casing member 12 may be closed by a metallic, electrically conductive, cup member 35 which may be spun or otherwise turned in about its periphery at 36 to. secure it to casing member 12 Disposed within cup 35 and adjacent the open end of casing member 12 is a thermally responsive, snap-acting element or disc 33. This disc ma, be of the bimetallic type shown and described in. United States Patent No. 1,448,240 to J. A. Spencer, issued March 13', 1923 Disc 38 is shown in Figs. 1 and 7 in a downwardly bowed condition. In response to an ambient temperature change this disc is effective to snap to the upwardly bowed condition or shape shown in Figs. 2 and 8. A transfer slide ffirides in and is guided by opposed recesses 41, 41 provided by casing member 12. One end 42 of transfer slide 40 is disposed in abutment with a central portion of disc 38, and the other end thereof provides, a flat surface 43 disposed adjacent bridging contact memberlf). As best shown in Figs. 2 and 4, contact member 20 provides opposed recesses 45, 45 with which-transfer member 40 interfits.

Bridging contact member 24 further provides a convexly curved surface 44 for cooperation with end surface 43. of transfer member 40. End surface 43 of transfer member 40 is engageable with convexly curved surface 44 substantially midway between spaced contacts 15 and 16. Surface 44.is convexly curved along a plane intersecting bridging contact member 20 and spaced contacts 15, 16. It will be apparent from Figs. 1 and 6 that corners 27, 27 engage convexly curved surface 25 one at each side of and adjacent to a vertical plane passing through the center or asis of curvature of surface 25 and through the mutually engaged portions of surfaces 43 and 44. Preferably, convexly curved surface 44 lies closely adjacent a plane which engages the surfaces of bridging contact member 20 that respectively engage contacts 15 and'16, and which plane lies normal to the opposite directions of movement of transfer member 40.

When disc 38-snaps in response to a temperature change to the upwardly bowed shape shown in Figs. 6 and.8, it quickly moves slide 40 and bridgingcontact member 20 against the resilient bias of spring 30 to separate. contact member'Zf) from spaced contacts 15 and'16. When disc 38 snaps back to the downwardly bowed condition shown in Figs. 1 and 7 in response to. a temperature change in the opposite direction, it permits contact member-'20and slide 40 to return quickly under the bias of springBO.

The cooperation between corners 27, 27 and'convexly curved surface 44, in part, provides a number of the features of thisinvention. Ifthe surface of oneof the contacts Her 16 should build-up more than the other or if the effective height of either of these contact surfaces should change relative to the other for any other reason, corners 27, 27 in association with surface 44 would permit bridging contact member 20 to pivot relative to cup-shaped member 26 during movement of'member 20 to the position shown in Figs. 1 and 7. That is, as bridging member 20 is moved downwardly to the position shown in Figs. 1 and 7, it would first engage the more built-up of the spaced contacts and the continued exertion of force by spring 30'would cause member 20 to pivot relative to cup-shaped member 26 until member 20 came into engagement with the lesser built-up of the spaced contacts. The effect of the cooperation between corners 27, 27 in association with convexly curved surface 44 in'combination with the resilient bias exerted by' spring. 30. against pivotal movement of cup-shaped member 26, results in the above-mentioned pivotal movement of bridging contact member without substantial concomitant movement of the cup-shaped member. This beingthe case, one side of spring 30 will not be compressedmorethan the. other and no resulting torque or moment will be exerted by the spring against bridging member 20 which would otherwise cause the latter to press with greater force on one of the. spaced, contacts than on the other. Another factor contributing to the feature of this invention that bridging member 20 presses with equal force against each of spaced contacts 15, 16, is that within the practical limits to which bridging member 29 is likely to pivot relative to cup-shaped member 26, both of corners 27, 27 will always engage convexly curved surface 25 closely. adjacent to and one on each side of the above-mentioned verticalplane which passes. through the axis or center of curvature of surface 25 and through the mutually engaged portions of surfaces 43 and 44. It follows that, thereby, the total pressing force exerted by bridging contact member 20 willbe equally divided between spaced contacts 15, 16- regardless of pivotal movement of contact member 20.

The importance of this balance of pressure against the respective spaced contacts becomes more apparent when it is realizedthat oftentimes this pressure-is no more'than several ounces; Even aslight imbalanceof pressurein such anenvironment wouldbesufficient drastically toaffect the conductivity of the. electrical connection between contact member 20 andeach of contacts-15 and' 16;

Since surface 43 of transfer member 40 is flat and since'surface 44. of bridging member 20- is convexly curved, no substantial torque or moment, due to a change in: the pivotal position of member 20, is exerted by the transfer member against the bridging member during operation of switch 10. This feature, per se, is conven tional as. shown, for example, by the United States patent to Wilms et al., No. 2,071,149, granted February 16, 1937, wherein the fiat surface of member 25 cooperates with convexlycurved surface 44 of bridging contact member 20. The novel combination of this oldstructure with the remainder. of the structure of the present invention, however, provides. further substantial advantages not available heretofore. construction wherebyv corners 27, 27 of switch 10 are associated with convexly curved surface-25 isrendered (due to the frictional effect between these corners 'and surface'25) capable of preventing pivotal movement of bridging. member 20 whenthe latter moves from andtoward engaged relation with contacts 15 and 16. Accordingly, contacts 15 and 16 will engage and disengage substantially simultaneously with contact member 20'. The simultaneity with which contacts 15 and 16 make and break connection with contact member 20 is further enhanced by, the present inventionfirstly because cup shapedzmember 26 is resiliently biased against pivotalmovement: by, spring Y30 and secondly because spring: 30,-- due tothedisclosed exemplary arrangementwhereby'it is laterally displaceable in'socket 31 and is unconfinedbetweenits ends, permits this cup-shaped member to be laterally-displaced without a tendency which would othen wise result toward pivotal movement of member-zflwhenf disengaged; from spaced contacts 15, 16; Obviously, if

member 20 should pivot relative to member 26 while separated, from contacts 15, 16', the resulting-lack; of simultaneityofrconnection between each. of contacts 15, 16 with contact member 20 isghighly undesirable.

To recapitulate briefly, it is apparent that, becausezcom' tact member 20 ispivotablej. as described above, equal contact pressures and simultaneous contact separation will be hadregardless of the relative heights: of contacts 15 and 16. So long-asthe relativeheightsofcontacts-15" and j 16 remain unchanged. this cqualityof pressures; and simultaneity of separation will be maintaineddueto :the'

frictional engagement of'corners 27, 27 "with surface.

Furthermore, upon a change in the effective height of one;

of contacts 15 and 1 6" with respecttothe other, pivotal movement of bridging contact member 201 will: result whereby equal contact pressures and simultaneous COD-e" tact separation will continue to be maintained.

The form and arrangement-of the above-describedistruo-Q ture is such as to constitute what-may; beconsideredito be an optimum relationship insofar as tending to In this regard, the" minimize the undesirable effects ofarcing. However, even with this optimum form'and arrangement of parts, particularly where terminals 13 and 14 are connected across a comparatively zhighzyol-tage source; these, undesirable efiects may stillioccur to some degree.

Oftentimes, when an arc is' struck between electrical contacts, the arcing may extend into the region immediately adjacent and surrounding -the-coacting surfaces of electrical contacts; in the case of the exemplary embodiment shown in the drawings, adjacent and surrounding the coacting surfaces of-contact member 20 and contacts 15 and 16. One of the common effects of this arcing is that a comparatively high heat is developed by theatre, which heat may be effective to vaporize'the material of which the contacts are formed. When the contact material vapon'zes, it emanates from the region immediately adjacent and surrounding the coacting surfaces of the contacts. The particles of this emanation travel along a substantially rectilinear path and are deposited on the structure of the device adjacent and exposed to this region. The greater the electrical conductivity of this deposit, the greater will be the tendency for the surface of any otherwise electrically insulating structure on which this material is deposited to act as a current-carrying conductor. It will be apparent that if such an electrically conductive deposit were formed on the adjacent surfaces of a casing member and/or an associated snap-acting member, an unintended electrically conductive path may thereby be set up. This might lead, for example, to unintentional grounding of one or more of the contacts of the electrical device. By way of example, if casing member 12 were not constructed and arranged according to this invention, an unintended electrically conductive path might be set up leading from any one of contacts 15, 16 or 20, along the interior surface of casing member 12 to cup 35 which would otherwise be electrically insulated from each of these contacts.

In the embodiment shown in the drawing the internal surface of casing member 12 provides two portions indicated generally by reference numerals 46 and 47, respectively. Each of surface portions 46 and 47 in this embodiment is continuous about the inner periphery of casing member 12 and is exposed to the above-mentioned region immediately adjacent and surrounding the coacting surfaces of the contacts. The surface portion of casing 12 which is intermediate surface portions 46 and 47 is configured to provide a projection 48. Adjacent projection 48 this intermediate surface portion provides a recess 49 whereby projection 48 lies between recess 49 and the above-mentioned region.

Since the arcing effect described above may extend into the region immediately adjacent and surrounding the coacting surfaces of contacts 15, 16 and 20, it will be apparent that with the exemplary construction shown in the drawing, projection 48 shields from this region at least that portion of the surface of easing member 12 which forms recess 49. Since the vaporized particles which emanate from the above-mentioned region travel in substantially a straight line, they will not be deposited on this shielded portion; or stated otherwise, these particles will not be deposited on at least a part of that portion of the internal surface of casing member 12 which lies intermediate surface portions 46 and 47. Accordingly, any otherwise possible electrically conductive path along the internal surface of casing member 12 leading from any one of contacts 15, 16 or 20 to cup 35 is discontinuous, thereby effectively preventing or counteracting the flow of electrical current from these contacts to the place occupied by cup 35.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results obtained.

The term contact as used throughout this specification is intended to encompass any means which is cooperative with another means to provide an electrically conductive path from one to the other and between and/ v first surface convexly curved along a plane intersecting said bridging contact member and said spaced contacts,

a transfer member having a flat surface movable against said convexly curved surface substantially midway between said spaced contacts to move said bridging contact member away from said spaced contacts in one of said opposite directions, an additional member providing a third surface convexly curved about an axis, said axis and the mutually engaged portions of said first and flat surfaces lying in a common plane, means resiliently biasing said additional member against pivotal movement and in the other of said opposite directions, and said bridging contact member providing two spaced corners engaging said third surface, one at each side of and adjacent to said common plane, whereby said bridging contact member presses with substantially equal force on each of said spaced contacts when engaged therewith and is prevented from pivotal movement relative to said third surface only when separated from said spaced contacts.

2. In combination, a pair of spaced electrical contacts, a bridging, electrical contact member movable in opposite directions into and out of engagement with said spaced contacts, said bridging contact member having a first surface convexly curved along a plane intersect ing said bridging contact member and said spaced con tacts, a transfer member having 'a flat surface movable against said convexly curved surface substantially midway between said spaced contacts to move said bridging contact member away from said spaced contacts in one of said opposite directions, an additional member providing a third surface convexly curved about an axis, said axis and the mutually engaged portions of said first and flat surfaces lying in a common plane, means permitting lateral displacement of said bridging contact member and resiliently biasing said additional member in the other of said opposite directions, and said bridging contact member providing two spaced corners engaging said third surface, one at each side of and adjacent to said common plane, whereby said bridging contact member presses with substantially equal force on each of said spaced contacts when engaged therewith and is prevented from pivotal movement relative to said third surface only when separated from said spaced contacts.

3. In combination; a pair of electrical contacts cooperable with each other to make and break an electrical circuit; a hollow casing member formed of electrically insulating material and surrounding said contacts; the interior surface of said casing being continuous about its periphery and, in cross-section, leading from a point adjacent the region immediately surrounding said contacts along a first length exposed to said region, then leading in a generally reverse direction behind the adjacent part of said first length from said region, and then leading in another generally reverse direction to extend along a second length and in substantially the same direction as said first length; and at least a portion of said second length being exposed to said region; whereby a peripherally continuous, interior surface area of said casing is shielded from said region.

4. The combination as set forth in claim 1 including a hollow casing member formed of electrically insulating material and surrounding said contacts, the interior surface'of said c'asingin'cluding two peripherally continuous, portions exposed tothe region immediately surrounding said contacts, one of said'surface portions lying. adjacent said contacts and the other being remote therefrom, said other surface portion being laterally displaced from said one surface portion in a direction away from said contacts, said surface portions being interconnected by a third peripherally continuous surface portion, said' third surface portion leading from said one surface portion in a reverse direction behind the adjacent part of said first portion from said contacts and then leading in another generally reverse direction to said other surface portion whereby said third surface portion provides a peripherany continuon'sIinteribr surface area" shielded. from said region;

References? Cited in: the file "of: this patent UNITED STATES PATENTS 1,988,369 Brown Jan. 15, 1935 2,094,199 Werner Sept. 28, 1937 2,392,342 Steinrnayer Jan. 8', 1946 2,570,610 Taylor Oct. 9, 1951 2,650,971 Dawe Sept. 1, 1953 2,714,643 Mitchell et a1 Aug; 2, 1955 2,740,869 Jennings Apr. 3, 1956- Mertler July 3, 1956 

